FeNeg function
FeNeg sets h = -f
Preconditions: |f| bounded by 1.12^25,1.12^24,1.12^25,1.12^24,etc.
Postconditions: |h| bounded by 1.12^25,1.12^24,1.12^25,1.12^24,etc.
Implementation
void FeNeg(FieldElement h, FieldElement f) {
h[0] = -f[0];
h[1] = -f[1];
h[2] = -f[2];
h[3] = -f[3];
h[4] = -f[4];
h[5] = -f[5];
h[6] = -f[6];
h[7] = -f[7];
h[8] = -f[8];
h[9] = -f[9];
}